In the fabrication process for semiconductor devices, numerous processing steps, i.e., as many as several hundred, must be carried out on a semi-conducting wafer to form device circuits. Of the numerous processing steps, photolithographic, etching, deposition, planarization and passivation steps are the most frequently performed on the wafer. After circuits are completely formed on the semiconductor device, the wafer must be tested to verify the proper function of the circuits before it is sliced into separate dies and packaged into chips. This type of testing is sometimes known as a known-good-die test (or KGD test) which is an important step in the total semiconductor manufacturing process for controlling the quality and reliability of the devices fabricated.
A known-good-die test can be carried out in many commercially available testing machines that are specifically designed for such purpose. For instance, one such tester is a Trillium.RTM. tester model Micro-Master II which is supplied by the LTX Corporation of San Jose, Calif. The Trillium.RTM. tester is normally used to electrically test semiconductor dies on a wafer to determine the individual die performance and subsequently, the wafer yields. When a die fails an electrical test, the testing machine places a round ink spot on the die so that the defective die can be readily identified and rejected in later chip handling process, i.e., wafer slicing and die sorting operations. After the slicing operation, the defective dies which have the ink spots are separated from the chips that have passed the electrical test.
While the Trillium.RTM.-type testing machines are effective in performing electrical tests to verify the proper functioning of the dies, certain other defects of the dies cannot be readily detected by the Trillium.RTM. tester. For instance, there may have been a defective passivation process which leads to dies that are insufficiently covered by an insulating layer as indicated by void formations. There may also be defects such as bonding pads that are defectively formed such that the die cannot be wire bounded in a later packaging process. These types of defects can be readily discovered by a visual examination of the dies by an operator looking at the wafer surface before the slicing operation during which the dies are severed into individual chips. When the defective dies are discovered during a visual examination, an ink mark must be manually placed on each of the defective dies by hand. Such manual inking process requires the use of a hand tool by an operator based on a die map for locating the defective dies and marking them with an ink spot.
Other defects for which the manual inking process must be carried out by using a hand tool include when the probe mark is out of specification, when the wafer surface is scratched, when the ink dot placed by the tester is cracked, smeared, splotched, diffused, when the ink formed a hollow ink dot with a void or when the ink dot size is out of specification.
The manual inking process performed by a quality inspector by using a hand tool can be defective in itself and thus causing various quality problems. For instance, the sizes of the ink dots are not the same when they are placed on defective dies by a human hand. Furthermore, the manual inking process carried out by using a hand tool also consumes unnecessary manpower and leads to longer cycle times. After the defective dies are manually inked by a hand tool, the wafer is sent to a bake oven for baking and drying. The manually placed ink dot frequently cracks after the baking process due to inadequate inking process or poor temperature control of the baking oven. Moreover, the manual inking process by a hand tool frequently requires a re-cleaning of the wafer surface or a re-inking of the defective dies.
It is therefore an object of the present invention to provide an apparatus for dispensing ink on an object that does not have the drawbacks or shortcomings of the conventional method of dispensing ink by a hand tool.
It is another object of the present invention to provide an apparatus for dispensing ink on an object by using an ink dispensing device slidingly supported by a guide rail system such that the ink dispensing device can be moved in both the X and Y directions on a guide rail system for placing ink dots on an object.
It is a further object of the present invention to provide an apparatus for dispensing ink on an object which includes an ink dispensing device mounted on a guide rail system for conveniently moving the ink dispensing device in the X and Y directions and then activating the dispensing of ink by an activation means.
It is another further object of the present invention to provide an apparatus for marking defective dies on a semiconductor wafer by using an ink dispensing device which is mounted on a guide rail system for two-dimensional movements of the dispensing device such that a defective die can be readily identified and located under the ink dispensing device.
It is still another object of the present invention to provide an apparatus for marking defective dies on a semiconductor wafer which includes an ink dispensing device mounted in a guide rail system for two-dimensional movement of the dispensing device and an activation device of a foot operated switch for controlling a pre-set flow of ink through the ink dispensing device.
It is yet another object of the present invention to provide an apparatus for marking defective dies on a semiconductor wafer by utilizing an ink dispensing device mounted on a guide rail system for two-dimensional movements of the dispensing device, an activation device for controlling the flow of ink through the dispensing device and a counter device for counting the number of times the activation device is activated.
It is still another further object of the present invention to provide a method for dispensing ink marks on a wafer surface by slidably mounting an ink dispensing device on a guide rail system for two-dimensional movements of the device and by activating the ink dispensing device for dispensing an ink drop after the device is moved to a predetermined location over a defective die.
It is yet another further object of the present invention to provide a method for dispensing ink marks on a semiconductor wafer surface by slidably mounting an ink dispensing device on a guide rail system for two-dimensional movements of the dispensing device and by calibrating a height of the ink dispensing device with a calibration stand prior to the start of each wafer marking process.